As shown in FIG. 1 and FIG. 2, a cab frame structure for a construction machine typically contains: front pillars 1 that are arranged to stand at left and right sides in front of a cab (a driver seat); roof pillars 2 that are extended from the top ends of the front pillars 1 backwardly and substantially horizontally; rear pillars 3 that are connected to the rear ends of the roof pillars 2 and extended downwardly therefrom; a front header 4 that is arranged to hang between the left and right front pillars 1 in the upper portions of the front pillars 1; and a rear header 5 that is arranged to hang between the left and right rear pillars 3 in the upper portions of the rear pillars 3.
A guide rail 6 is placed in the front pillar 1 and the roof pillar 2. Members to be guided 8 (as one example, a guide roller, a projection and the like) attached to a front window unit 7 are engaged with these guide rails 6. Since the members to be guided 8 are guided by the guide rails 6, the front window unit 7 is moved along the front pillars 1 and the roof pillars 2 and switched between a closed position where the front window unit 7 is supported in a standing state in the front pillars 1 and an opened position where the front window unit 7 is supported in a horizontal state in the roof pillars 2 and consequently opens and closes the front surface of the cab. The front header 4 is arranged coincidentally with the position of the top end of the front window unit 7 set at the closed position.
By the way, as the cab frame structure for the construction machine of this kind, a structure in which, since the front pillar 1 and the roof pillar 2 are configured by one curved tubular material 9, a strength is improved and a good outward appearance is improved is known (refer to a patent document 1).